Ionically and covalently cross-linked polymers and polymer membranes

ABSTRACT

The present invention relates to ionically and covalently cross-linked polymers and polymer membranes having recurrent units of the general formula (1), wherein Q is a link, oxygen, sulfur, (2) or (3) and the R radical is a divalent radical of an aromatic or heteroaromatic compound, and which are characterized in that a) R radical comprises at least partially substituents of general formula (4A), (4B), (4C), (4D), (4E), (4F), (4G) and/or (4H), b) R radical comprises at least partially substituents of the general formula (5A) and/or (5B) and/or the R radical is at least partially a group of the general formula (5C) and/or (5D) and c) the R radical comprises at least partially bridges of the general formula (6) linking at least to R radicals together, R 1 , R 2 , R 3 , R 4 , R 5 , M, X, Y, Z and m having the herein-mentioned meanings.

This application claims the benefit under §365c of PCT/EP01/05644 filedMay 17, 2001, which was published under PCT 21(2) in German.

The present invention relates to covalently and ionically crosslinkedpolymers, particularly to covalently and ionically crosslinked polymerscomprising repeating units of the general formula

—Q—R  (1)

in which Q is a bond, oxygen, sulfur,

the radical R is a divalent radical of an aromatic or heteroaromaticcompound. The present invention further describes a process forpreparing the covalently and ionically crosslinked polymers and alsotheir use, particularly in fuel cells.

Polymers with repeating units of the general formula (I) are alreadyknown. They include, for example, polyarylenes, such as polyphenyleneand polypyrene, aromatic polyvinyl compounds, such as polystyrene andpolyvinylpyridine, polyphenylenevinylene, aromatic polyethers, such aspolyphenylene oxide, aromatic polythioethers, such as polyphenylenesulfide, polysulfones, such as ®Radel R, and polyether ketones, such asPEK. Moreover, they also embrace polypyrroles, polythiophenes,polyazoles, such as polybenzimidazole, polyanilines, polyazulenes,polycarbazoles, and polyindophenines.

Recently, the use of such polymers for producing membranes for use infuel cells has become increasingly important. Polymers with basicgroups, such as sulfonic acid groups and amino groups, in particular,are increasingly being described in the literature. The membranes aredoped with concentrated phosphoric acid or sulfuric acid and serve asproton conductors in what are known as polyelectrolyte membrane fuelcells (PEM fuel cells). Such membranes allow the membrane electrodeassembly (MEA) to be operated at relatively high temperatures and soincrease the tolerance of the catalyst significantly toward the carbonmonoxide which is produced as a by-product in the reformation, therebysubstantially simplifying the reprocessing or purification of gas.Disadvantages of these membranes are their mechanical instability, witha low modulus of elasticity, a low tensile strength, and a low upperflow limit, and their relatively high permeability to hydrogen, oxygen,and methanol.

First attempts to solve these problems are disclosed in the documents DE196 22 337, WO 99/02755, and WO 99/02756. DE 196 22 337 describes aprocess for producing covalently crosslinked ionomer membranes which isbased on an alkylation reaction of sulfinate-functional polymers,polymer blends, and polymer (blend) membranes. The covalent network isresistant to hydrolysis even at relatively high temperatures. Adisadvantage, however, is that, owing to the hydrophobic covalentnetwork, the covalently crosslinked ionomers and ionomer membranes dryout easily and may therefore undergo severe embrittlement; as a result,they are of only limited suitability for applications in fuel cells,especially at relatively high temperatures.

The documents WO 99/02756 and WO 99/02755 disclose ionically crosslinkedacid-base polymer blends and polymer (blend) membranes. One advantage ofthe ionically crosslinked acid-base blend membranes is that the ionicbonds are flexible, even at relatively high temperatures thepolymers/membranes do not dry out so easily, owing to the hydrophilicityof the acid-base groups, and therefore the polymers/membranes do notundergo embrittlement even at relatively high temperatures. Theionically crosslinked ionomer (membrane) systems described in thesedocuments, however, have the disadvantage that the ionic bonds part inthe temperature range between 60 and 90° C. and from this temperaturerange on the polymers/membranes begin exorbitantly to swell.Consequently, these membranes too are poorly suited to applications infuel cells, especially at relatively high temperatures upward of 80° C.

In the light of the prior art it is now an object of the presentinvention to provide a crosslinked polymer having improved properties.The polymer of the invention is to have a low specific volumeresistance, preferably less than or equal to 100 Ωcm at 25° C., and toexhibit low permeability for hydrogen, oxygen, and methanol.

Furthermore, it is to have a very good mechanical stability, inparticular an improved modulus of elasticity, a higher tensile strength,and improved swelling properties. It should preferably swell by lessthan 100% in deionized water at a temperature of 90° C.

A further object was to specify a crosslinked polymer which can be usedin fuel cells. The crosslinked polymer ought in particular to besuitable for use in fuel cells upward of 80° C., in particular upward of100° C.

A further object of the invention was to provide a process for preparingthe crosslinked polymer that can be carried out simply, inexpensively,and on an industrial scale.

These objects and further objects, which are not mentioned explicitlybut can readily be derived or inferred from the circumstances discussedintroductorily herein, are achieved by means of a covalently andionically crosslinked polymer having all of the features of claim 1.Appropriate modifications of the crosslinked polymer of the inventionare protected in the subclaims which refer back to claim 1. Processesfor preparing the crosslinked polymer of the invention are described inthe process claims, while the claims of the use category protectpreferred uses of a crosslinked polymer of the invention.

By virtue of the fact that a covalently and ionically crosslinkedpolymer comprising repeating units of the general formula (I) is madeavailable which is distinguished in that

a) the radical R has at least in part substituents of the generalformula (4A), (4B), (4C), (4D), (4E), (4F), (4G) and/or (4H)

where the radicals R¹ independently of one another are a bond or a grouphaving 1 to 40 carbon atoms, preferably a branched or unbranched alkylor cycloalkyl group or an optionally alkylated aryl group,

M is hydrogen, a metal cation, preferably Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, or anoptionally alkylated ammonium ion, and

X is a halogen or an optionally alkylated amino group,

b) the radical R has at least in part substituents of the generalformula (5A) and/or (5B)

in which R², R³, R⁴ and R⁵ independently of one another are a grouphaving from 1 to 40 carbon atoms, preferably a branched or unbranchedalkyl or cycloalkyl group or an optionally alkylated aryl group, itbeing possible for at least two of the radicals R², R³, and R⁴ to beclosed to form an optionally aromatic ring,

and/or the radical R is at least in part a group of the general formula(5C) and/or (5D)

and

c) the radical R has at least in part bridges of the general formula (6)

which join at least two radicals R to one another,

Y being a group having from 1 to 40 carbon atoms, preferably a branchedor unbranched alkyl or cycloalkyl group or an optionally alkylated arylgroup,

Z is hydroxyl, a group of the general formula

or a group having a molecular weight of more than 20 g/mol, composed ofthe optional components H, C, O, N, S, P, and halogen atoms, and

m is an integer greater than or equal to 2,

it is possible in a manner which was not immediately foreseeable to makeavailable a crosslinked polymer having improved mechanical properties,in particular a higher modulus of elasticity, an improved tensilestrength, and improved swelling properties.

At the same time the crosslinked polymer of the invention display anumber of further advantages. These include, among others:

The doped polymer membranes have a low specific volume resistance,preferably less than or equal to 100 Ωm at 25° C.

The doped polymer membranes possess only a low permeability forhydrogen, oxygen and methanol.

Even an extremely thin membranes of the crosslinked polymer of theinvention, with a total thickness of between 10 and 100 μm, possesssufficiently good material properties at 80° C., in particular a veryhigh mechanical stability and a low permeability for hydrogen, oxygenand methanol.

The doped polymer membrane is suitable for use in fuel cells upward of80° C., in particular under standard pressure.

The doped polymer membrane can be produced simply, on an industrialscale, and inexpensively.

In accordance with the present invention the polymer is ionically andcovalently crosslinked. In accordance with the invention, crosslinkedpolymers are those polymers whose linear or branched macromolecules,which are of the same or different chemical identity and are present inthe form of collectives, are linked to one another to formthree-dimensional polymer networks. In this case the crosslinking may beeffected both by way of the formation of covalent bonds and by way ofthe formation of ionic bonds. Further details may be taken from thetechnical literature, examples being C D Römpp Chemie Lexikon—Version1.0, Stuttgart/New York: Georg Thieme Verlag 1995, entry on“Crosslinking” and the literature cited in that section.

The crosslinked polymer of the invention has repeating units of thegeneral formula (1), especially repeating units corresponding to thegeneral formulae (1A), (1B), (1C), (1D), (1E), (1F), (1G), (1H), (1),(1J), (1K), (1L), (1M), (1N), (1O), (1P), (1Q), (1R), (1S) and/or (1T):

Independently of one another here the radicals R⁶ which are identical ordifferent, are 1,2-phenylene, 1,3-phenylene, 1,4-phenylene,4,4′-biphenyl, a divalent radical of a heteroaromatic, a divalentradical of a C₁₀ aromatic, a divalent radical of a C₁₄ aromatic and/or adivalent pyrene radical. An example of a C₁₀ aromatic is naphthalene; ofa C₁₄ aromatic, phenanthrene. The substitution pattern of the aromaticand/or heteroaromatic is arbitrary, in the case of phenylene, forexample, R⁶ may be ortho-, meta- and para-phenylene.

The radicals R⁷, R⁸, and R⁹ designate monovalent, tetravalent andtrivalent aromatic or heteroaromatic groups, respectively, and theradicals U, which are identical within a repeating unit, are an oxygenatom, a sulfur atom or an amino group which carries a hydrogen atom, agroup having 1-20 carbon atoms, preferably a branched or unbranchedalkyl or alkoxy group, or an aryl group as a further radical.

The polymers with repeating units of the general formula (1) that areparticularly preferred in the context of the present invention includehomopolymers and copolymers, examples being random copolymers, such as®Victrex 720 P and ®Astrel. Especially preferred polymers are polyarylethers, polyaryl thioethers, polysulfones, polyether ketones,polypyrroles, polythiophenes, polyazoles, phenylenes,polyphenylenevinylenes, polyanilines, polyazulenes, polycarbazoles,polypyrenes, polyindophenines and polyvinylpyridines, especiallypolyaryl ethers:

Especially preferred in accordance with the invention are crosslinkedpolymers with repeating units of the general formula (1A-1), (1B-1),(1C-1), (1I-1), (1G-1), (1E-1), (1H-1), (1I-1), (1F-1), (1J-1), (1K-1),(1L-1), (1M-1) and/or (1N-1).

In the context of the present invention, n designates the number ofrepeating units along one macromolecule chain of the crosslinkedpolymer. This number of the repeating units of the general formula (1)along one macromolecule chain of the crosslinked polymer is preferablyan integer greater than or equal to 10, in particular greater than orequal to 100. The number of repeating units of the general formula (1A),(1B), (1C), (1D), (1E), (1F), (1G), (1H), (1I), (1J), (1K), (1L), (1M),(1N), (1O), (1P), (1Q), (1R), (1S) and/or (1T) along one macromoleculechain of the crosslinked polymer is preferably an integer greater thanor equal to 10, in particular greater than or equal to 100.

In one particularly preferred embodiment of the present invention, thenumerical average of the molecular weight of the macromolecule chain isgreater than 25,000 g/mol, appropriately greater than 50,000 g/mol, inparticular greater than 100,000 g/mol.

The crosslinked polymer of the invention may in principle also containdifferent repeating units along a macromolecule chain. Preferably,however, along one macromolecule chain it contains only identicalrepeating units of the general formula (1A), (1B), (1C), (1D), (1E),(1F), (1G), (1H), (1I), (1J), (1K), (1L), (1M), (1N), (1O), (1P), (1Q),(1R), (1S) and/or (1T).

In the context of the present invention the radical R has at least inpart substituents of the general formula (4A), (4B), (4C), (4D), (4E),(4F), (4G) and/or (4H), preferably of the general formula (4A), (4B),(4C) and/or (4D), appropriately of the general formula (4A), (4B) and/or(4C), in particular of the general formula (4A):

Here, the radicals R¹ independently of one another designate a bond or agroup having from 1 to 40 carbon atoms, preferably a branched orunbranched alkyl or cycloalkyl group or an optionally alkylated arylgroup. In the context of one especially preferred embodiment of thepresent invention, R¹ is a bond.

M stands for hydrogen, a metal cation, preferably Li⁺, Na⁺, K⁺, Rb⁺,Cs⁺, or an optionally alkylated ammonium ion, appropriately for hydrogenor Li⁺, in particular for hydrogen.

X is a halogen or an optionally alkylated amino group.

Moreover, in accordance with the invention, the radical R has at leastin part substituents of the general formula (5A) and/or (5B), preferably(5A)

and/or the radical R is at least in part a group of the general formula(5C) and/or (5D), preferably (5C).

In this context the radicals R², R³, R⁴ and R⁵ independently of oneanother denote a group having from 1 to 40 carbon atoms, preferably abranched or unbranched alkyl or cycloalkyl group or an optionallyalkylated aryl group, it being possible for at least two of the radicalsR², R³ and R⁴ to be closed to form an optionally aromatic ring.

Particularly advantageous effects can be achieved if R has at least inpart substituents of the general formula (5A-1) and/or (5A-2).

Here, the radicals R¹⁰ denotes an optionally alkylated aryl group, whichcontains at least one optionally alkylated amino group, or an optionallyalkylated heteroaromatic, which either has at least one optionallyalkylated amino group or has at least one nitrogen atom in theheteroaromatic nucleus. R¹¹ is hydrogen, an alkyl, cycloalkyl, aryl orheteroaryl group or a radical R¹⁰ with the definition specified above,it being possible for R¹⁰ and R¹¹ to be identical or different.

Especially preferred in accordance with the invention are substituentsof the formula (5A-1) in which R¹⁰ is an optionally alkylated anilineradical or pyridine radical, preferably an alkylated aniline radical.Moreover, particular preference is also given to substituents of theformula (5A-2) in which R¹⁰ and R¹¹ are optionally alkylated anilineradicals or pyridine radicals, preferably alkylated aniline radicals.

In the context of the present invention the radical R has at least inpart bridges of the general formula (6)

which join at least two radicals R to one another, Y being a grouphaving 1 to 40 carbon atoms, preferably a branched or unbranched alkylor cycloalkyl group or optionally alkylated aryl group, appropriately alinear or branched alkyl group containing from 1 to 6 carbon atoms.

Z designates hydroxyl, a group of the general formula

or a group having a molecular weight of more than 20 g/mol composed ofthe optional components H, C, O, N, S, P and halogen atoms, and m standsfor an integer greater than or equal to 2, preferably 2.

The crosslinked polymer of the invention is preferably are doped withacid. In the context of the present invention, doped polymers are thosepolymers which owing to the presence of doping agents exhibit anincreased proton conductivity in comparison with the undoped polymers.Dopants for the polymers of the invention are acids. Acids in thiscontext embrace all known Lewis and Brønsted acids, preferably inorganicLewis and Brønsted acids. Also possible is the use of polyacids,especially isopolyacids and heteropolyacids, and mixtures of differentacids. For the purposes of the present invention, heteropolyacids areinorganic polyacids having at least two different central atoms whichare formed as partial mixed anhydrides from in each case weak polybasicoxygen acids of a metal (preferably Cr, Mo, V, W) and of a nonmetal(preferably As, I, P, Se, Si, Te). They include, among others,12-molybdatophosphoric acid and 12-tungstophosphoric acid.

Dopants which are particularly preferred in accordance with theinvention are sulfuric acid and phosphoric acid. One especiallypreferred dopant is phosphoric acid (H₃PO₄).

By way of the degree of doping it is possible to influence theconductivity of the polymer membrane of the invention. As theconcentration of dopant goes up, the conductivity increases until amaximum is reached. In accordance with the invention, the degree ofdoping is reported as mole acid per mole repeating unit of the polymer.In the context of the present invention a degree of doping of between 3and 15, in particular between 6 and 12, is preferred.

Processes for preparing doped polymer membrane are known. In onepreferred embodiment of the present invention they are obtained bywetting a polymer of the invention for an appropriate time, preferably0.5-96 hours, with particular preference 1-72 hours, at temperaturesbetween room temperature and 100° C. and, where appropriate, underelevated pressure with concentrated acid, preferably with highlyconcentrated phosphoric acid.

The spectrum of properties of the crosslinked polymer of the inventioncan be modified by varying its ion exchange capacity. The ion exchangecapacity lies preferably between 0.5 meq/g and 1.9 meq/g, based in eachcase on the total mass of the polymer.

The polymer of the invention has a low specific volume resistance,preferably of not more than 100 Ωcm, appropriately of not more than 50Ωcm, in particular of not more than 20 Ωcm, in each case at 25° C.

The properties of the polymer membrane of the invention may becontrolled in part by its total thickness. Nevertheless, even extremelythin polymer membranes possess very good mechanical properties andrelatively low permeability for hydrogen, oxygen, and methanol. They aretherefore suitable for use in fuel cells upward of 80° C., appropriatelyupward of 100° C., and in particular for use in fuel cells upward of120° C., without it being necessary to reinforce the edge region of themembrane electrode assembly. The total thickness of the doped polymermembrane of the invention is preferably between 50 and 100 μm,appropriately between 10 and 90 μm, in particular between 20 and 80 μm.

In the context of one especially preferred embodiment of the presentinvention it swells by less than 100% in deionized water at atemperature of 90° C.

Processes for preparing the crosslinked polymer of the invention areobvious to the person skilled in the art. Nevertheless, in the contextof the present invention a procedure which has proven especiallysuitable is that in which one or more precursor polymers whichindividually or in toto contain the functional groups a), b) and d), d)designating sulfinate groups of the general formula (6)

is or are reacted with a compound of the general formula (7)

YL_(m)  (7)

where L is a leaving group, preferably an F, Cl, Br, I, tosylate, and nis an integer greater than or equal to 2, preferably 2. Each precursorpolymer preferably has repeating units of the general formula (1).Furthermore, appropriately, it is not covalently crosslinked.

Where in at least one precursor polymer the radical R has at least inpart substituents of the general formula (5A) or is at least in part agroup of the general formula (5C), the reaction with the compound (7)may also, moreover, lead to the formation of bridges of the generalformula (8) and/or (9).

Also conceivable is the formation of bridges between differentsubstituents of the general formula (5A) and/or between different groupsof the general formula (5C).

In one particularly preferred embodiment of the present invention apolymer mixture is used comprising

1) at least one precursor polymer having functional groups a),

2) at least one precursor polymer having functional groups b), and

3) at least one precursor polymer having functional groups d).

In another particularly preferred embodiment of the present invention apolymer mixture is used comprising

1) at least one precursor polymer having functional groups a) and b) and

2) at least one precursor polymer having functional groups d).

In accordance with another particularly preferred embodiment of thepresent invention it may also be particular advantageous to use apolymer mixture comprising

1) at least one precursor polymer having functional groups a) and d) and

2) at least one precursor polymer having functional groups b).

Furthermore, processes wherein use is made of a polymer mixturecomprising

1) at least one precursor polymer having functional groups a) and

2) at least one precursor polymer having functional groups b) and d)

also constitutes a particularly preferred embodiment of the presentinvention.

In accordance with the invention it may also be exceptionallyappropriate to use at least one polymer having functional groups of thegeneral formula a), b) and d).

The precursor polymer or polymers for use in accordance with theinvention may in principle have different repeating units of the generalformula (1). Preferably, however, they have only identical repeatingunits of the general formula (1A), (1B), (1C), (1D), (1E), (1F), (1G),(1H), (1I), (1J), (1K), (1L), (1M), (1N), (1O), (1P), (1Q), (1R), (1S)and/or (1T).

The number of repeating units of the general formula (1A), (1B), (1C)(1D), (1E), (1F), (1G) (1H), (1I), (1J), (1K), (1L), (1M), (1N), (1O),(1P), (1Q) (1R), (1S) and/or (1T) is preferably an integer greater thanor equal to 10, preferably at least 100 repeating units.

In one particularly preferred embodiment of the present invention thenumerical average of the molecular weight of the precursor polymer orpolymers is greater than 25,000 g/mol, appropriately greater than 50,000g/mol, in particular greater than 100,000 g/mol.

The synthesis of the precursor polymers having functional groups of thegeneral formula a), b) and/or d) is already known. It can take place,for example, by reacting a polymer of the general formula (1) withn-butyllithium in a dried aprotic solvent, preferably tetrahydrofuran(THF), under an inert gas atmosphere, preferably argon, and solithiating it.

In order to introduce the functional groups, the lithiated polymer is[lacuna] in a manner known per se with suitable functionalizing agents,preferably with alkylating agent of the general formula

L-Subst.  (10)

where Subst. is the substituent to be introduced; with ketones and/oraldehydes, which are reacted to the corresponding alkoxides; and/or withcarboxylic esters and/or carbonyl halides, which are reacted to thecorresponding ketones. The introduction of sulfonate groups may also beeffected by reacting the lithiated polymer with SO₃, and theintroduction of sulfinate groups by reacting the lithiated polymer withSO₂.

Through successive reaction with two or more different functionalizingagents, polymers are obtained which have at least two differentsubstituents.

For further details, refer to the state of the art, in particular to thedocuments U.S. Pat. No. 4,833,219, J. Kerres, W. Cui, S. Reichle; Newsulfonated engineering polymers via the melation route. 1. Sulfonatedpoly-(ethersulfone) PSU Udel® via metalation-sulfination-oxidation” J.Polym. Sci.: Part A: Polym. Chem. 34, 2421-2438 (1996), WO 00/09588 A1,whose disclosure content is hereby explicitly incorporated by reference.

The degree of functionalization of the precursor polymers liespreferably in the range from 0.1 to 3 groups per repeating unit,preferably between 0.2 and 2.2 groups per repeating unit. Particularpreference is given to precursor polymers having from 0.2 to 0.8 groupsa), preferably sulfonate groups, per repeating unit. Moreover, precursorpolymers having from 0.8 to 2.2 groups b) per repeating unit have beenfound particularly appropriate. Moreover, particularly advantageousresults are achieved with precursor polymers which have from 0.8 to 1.3groups d) per repeating unit.

In the context of the present invention it has proven especiallyappropriate to dissolve the precursor polymer or polymers in adipolar-aprotic solvent, preferably in N,N-dimethylformamide,N,N-dimethyl-acetamide, N-methylpyrrolidone, dimethyl sulfoxide orsulfolane, and to react the solution with the halogen compound, withstirring.

Particularly advantageous results can be achieved here if

a) the polymer solution is spread as a film on a substrate, preferablyon a glass plate or a woven or nonwoven fabric, and

b) the solvent is evaporated, where appropriate at an elevatedtemperature of more than 25° C. and/or under a reduced pressure of lessthan 1000 mbar, to give a polymer membrane.

The properties of the polymer of the invention may also be enhanced by

a) treating the polymer in a first step with an acid and

b) treating the polymer in a further step with deionized water,

the polymer being treated where appropriate with an aqueous alkali priorto the first step.

Possible fields of use for the covalently and ionically crosslinkedpolymer of the invention are evident to the skilled worker. It isparticularly suitable for all applications which are indicated forcrosslinked polymers having low specific volume resistances, preferablyless than 100 Ωcm at 25° C. On the basis of their characteristicproperties, they are suitable in particular for applications inelectrochemical cells, preferably in secondary batteries, electrolysiscells, and in polymer electrolyte membrane fuel cells, especially inhydrogen fuel cells and direct methanol fuel cells.

Moreover, they may also be employed to particular advantage in membraneseparation operations, preferably in the context of gas separation,pervaporation, perstraction, reverse osmosis, nanofiltration,electrodialysis, and diffusion dialysis.

The invention is illustrated in more detail below using examples andcomparative examples, without any intention that the teaching of theinvention should be restricted to these examples. The property valuesreported, like the values described above, were determined as follows:

In order to determine the ion exchange capacity, IEC, a piece ofprotonated ionomer membrane was dried to constant weight. 1 mg of themembrane was introduced into about 50 ml of saturated NaCl solution. Asa result, there was ion exchange of the sulfonate groups, with the H⁺ions passing into the saturated solution. The solution with the membranewas shaken or stirred for about 24 hours. Thereafter, 2 drops of theindicator bromothymol blue were added to the solution, which wastitrated with 0.1-normal NaOH solution until the change of color fromyellow to blue. The IEC was calculated as follows:

IEC[meq/g]=(normality of NaOH[meq/ml]*consumption of NaOH[ml]*factor ofNaOH)/mass of membrane[g]

The specific volume resistance R^(sp) of the membranes was determined bymeans of impedance spectroscopy (IM6 impedance meter, Zahner elektrik)in a Plexiglas unit with gold-coated copper electrodes (electrode area0.25 cm²). Here, in accordance with the invention, the impedance atwhich the phase angle between current strength and voltage was 0designates the specific volume resistance. The actual measurementconditions were as follows: 0.5 N HCl was used, the membrane undermeasurement was packed between two Nafion 117 membranes, and themultilayer arrangement of Nafion 117/membrane/Nafion 117 membrane waspressed between the two electrodes. In this way, the interfacialresistances between membrane and electrode were eliminated by measuringfirst of all the multilayer arrangement of all three membranes and thenthe two Nafion 117 membranes alone. The impedance of the Nafionmembranes was substrated from the impedance of all three membranes. Inthe context of the present invention the specific volume resistanceswere determined at 25° C.

In order to determine the swelling, the membranes were equilibrated indeionised water at the respective temperature and then weighed(=m^(swollen)). The membranes were then dried at elevated temperature ina drying oven and weighed again (=m^(dry)). The degree of swelling iscalculated as follows:

Q=(m ^(swollen) −m ^(dry))/m ^(dry)

a) polymers used

a-1) PSU Udel®

PSU P 1800 (Amoco)

a-2) PEK-SO₃Li:

Lithium salt of sulfonated polyether ketone PEK;

Preparation:

100 g of PEK-SO₃H having an ion exchange capacity of 1.8 meq SO₃H/gpolymer were stirred for 24 hours in 1000 ml of a 10% strength by weightaqueous LiOH solution. Thereafter the Li-exchanged PEK-SO₃Li wasfiltered off, washed with water until the wash water gave a neutralreaction, and then dried at 100° C. for 48 h. The resulting polymercontained 0.4 SO₃Li units per repeating unit (ion exchange capacity(IEC) of the protonated form=1.8 meq SO₃H/g).

a-3) PSU-SO₂Li:

Lithium salt of sulfinated polyether sulfone PSU Udel®

obtained in accordance with U.S. Pat. No. 4,833,219 or J. Kerres, W.Cui, S. Reichle; New sulfonated engineering polymers via the melationroute. 1. Sulfonated poly(ethersulfone) PSU Udel® viametalation-sulfination-oxidation” J. Polym. Sci.: Part A: Polym. Chem.34, 2421-2438 (1996) IEC of the protonated form=1.95 meq SO₂Li/g

a-4) PSU-DPK:

obtained by reacting 2,2′-dipyridyl ketone with lithiated PSU Udel (inaccordance with WO 00/09588 A1);

one 2,2′-dipryidyl ketone unit per repeating unit.

a-5) Synthesis of PSU-P3-SO₂Li, PSU-EBD-SO₂Li PSU-P3-SO₂Li,

First of all PSU Udel® was dissolved in dry THF and the solution wascooled to −75° C. under argon. Traces of water in the reaction mixturewere removed with 2.5 M n-butyllithium (n-BuLi). The dissolved polymerwas subsequently lithiated with 10 M n-BuLi. The batch was left to reactfor one hour and then pyridine-3-aldehyde or4,4′-bis(N,N-diethylamino)benzo-phenone was added. The reactiontemperature was thereafter raised to −20° C. for one hour. For thereaction with SO₂ it was subsequently cooled again to −75° C. and theSO₂ was passed in.

For working up, 10 ml of an isopropanol/water mixture was introduced bysyringe into the reaction solution, which was heated to roomtemperature, and the polymer was precipitated in an excess ofisopropanol, and the resulting polymer was filtered off and washed,where appropriate with isopropanol. For purification, the polymer wassuspended in methanol and filtered off again. The polymer was dried invacuo, preferably at 80° C. The degrees of substitution were obtained byquantitative evaluation of the ¹H-NMR spectra.

TABLE 1 Synthesis of PSU-P3-SO₂Li and PSU-EBD-SO₂Li Degree ofsubstitution per Batch repeating unit PSU-P3-SO₂Li 10 ml 10 M BuLi 0.8pyridine-3- 1000 ml THF aldehyde 22.1 g PSU Udel ® 1.2 SO₂Li 5.35 gpyridine-3- aldehyde SO₂ PSU-DEB-SO₂Li 10 ml 10 M BuLi 0.4 4,4-Bis(N,N-1000 ml THF diethylamino)benzo 22.1 g PSU Udel ® phenone 16.22 g4,4′-bis- 1.6 SO₂Li (N,N-diethylamino)- benzophenone SO₂

b.) Membrane Production

The polymers PEK-SO₃Li, PSU-P3-So₂Li, PSU-EBD-SO₂Li, PSU-DPK and/orPSUSO₂Li were dissolved in NMP in accordance with Table 2 and filtered.The polymer solution was then degassed in vacuo and subsequently admixedwith 1,4-diiodobutane. It was subsequently poured onto a glass plate anddrawn but using a doctor blade. The glass plate was dried in an oven at60° C. for 1 hour, then at 90° C. for a further hour and finally at 120°C. under vacuum overnight. The plate was cooled to room temperature andplaced in a waterbath. The membrane was separated from the glass plateand stored in 10% HCl in an oven at 90° C. for one day. It wassubsequently conditioned in deionized water at 60° C.

c.) Characterization of the Membranes

The characteristic data of the membranes are summarized in Tables 2 and3. The theoretical ion exchange capacity IEC^(theo) was calculatedtaking into account both the ionic and the covalent crosslinking. FromTable 3 it is evident that the covalently and ionically crosslinkedmembranes have much lower swelling figures than the purely ionicallycrosslinked membranes, and this is so even at temperatures of 90° C.

TABLE 2 Membrane characteristic data Thickness IEC^(exp) IEC^(theo)R^(sp) Membrane Composition [μm] [meq/g] [meq/g] [Ωcm] Example 0.77 gPSU-EBP 64 1.03 1.09 6.87 1 2.0 g PEK-SO₃Li (wz054) 0.6 g 1,4-diiodobutane Example 0.77 g PSU-Pe 87 0.81 0.88 3.62 2 2.0 g PEK-SO₃Li(wz051) 0.48 g 1,4- diiodobutane Example 3 g PEK-SO₃Li 113 1.43 1.4 13.43 0.3 g PSUSO₂Li (wz40) 0.3 g PSU-DPK 0.205 ml 1,4- diiodobutane Example1 g PEK-SO₃Li 52 0.86 0.89 35.96 4 0.3 g PSUSO₂Li (wz40R) 0.3 g PSU-DPK0.205 ml 1,4- diiodobutane Compar- 3 g PEK-SO₃Li 126 1.52 1.52 7.8 ative1 0.3 g PSU-DPK (wz43) Compar- 1 g PEK-SO₃Li 56 0.92 0.79 24.5 ative 20.5 g PSU-DPK (wz43R) Compar- PEK-SO₃H 82 1.63 1.8 7.13 ative 3

IEC^(exp): experimentally determined ion exchange capacity

R^(SP): specific volume resistance

TABLE 3 Swelling characteristics of the membranes in water as a functionof temperature Swelling in [%] Membrane 25° C. 40° C. 60° C. 90° C.Example 1 40.79 46.05 46.05 59.21 (wz054) Example 2 38.46 44.61 44.6161.54 (wz051) Example 3 42 42.48 58.41 151.33 (wz40) Example 4 22.9 27.129.2 35.9 (wz40R) Comparative 1 95.9 110.4 161.09 224.43 (wz43)Comparative 2 29 33.77 34.2 48.05 (wz43R) Comparative 3 107.32 122129.27 139.02 PEK-SO₃H

What is claimed is:
 1. A covalently and ionically crosslinked polymer,having repeating units of the general formula —Q—R—  (1) in which Q is:a bond; oxygen; sulfur;

or

and, the radical R is a divalent radical of an aromatic orheteroaromatic compound, characterized in that (a) the radical R has atleast in part substituents of the general formula (4A), (4B), (4C),(4D), (4E), (4F), (4G) and/or (4H)

where the radicals R¹ independently of one another are a bond or a grouphaving 1 to 40 carbon atoms, preferably a branched or unbranched alkylor cycloalkyl group or an optionally alkylated aryl group, M ishydrogen, a metal cation, preferably Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, or anoptionally alkylated ammonium ion, and X is a halogen or an optionallyalkylated amino group, (b) the radical R has at least in partsubstituents of the general formula (5A) and/or (5B)

in which R², R³, R⁴ and R⁵ independently of one another are a grouphaving from 1 to 40 carbon atoms, preferably a branched or unbranchedalkyl or cycloalkyl group or an optionally alkylated aryl group, itbeing possible for at least two of the radicals R², R³, and R⁴ to beclosed to form an optionally aromatic ring, and/or the radical R is atleast in part a group of the general formula (5C) and/or (5D)

and (c) the radical R has at least in part bridges of the generalformula (6)

which join at least two radicals R to one another, Y being a grouphaving from 1 to 40 carbon atoms, preferably a branched or unbranchedalkyl or cycloalkyl group or an optionally alkylated aryl group, Z ishydroxyl, a group of the general formula

or a group having a molecular weight of more than 20 g/mol, composed ofthe optional components H, C, O, N, S, P, and halogen atoms, and m is aninteger greater than or equal to
 2. 2. The polymer of claim 1,characterized in that the repeating units of the general formula (1) areunits corresponding to the general formulae (1A), (1B), (1C), (1D),(1E), (1F), (1G), (1H), (1I), (1J), (1K), (1L), (1M), (1N), (1O), (1P),(1Q), (1R), (1S) and/or (1T)

in which the radicals R⁶ independently of one another, which areidentical or different, are 1,2-phenylene, 1,3-phenylene, 1,4-phenylene,4,4′-biphenyl, a divalent radical of a heteroaromatic, a divalentradical of a C₁₀ aromatic, a divalent radical of a C₁₄ aromatic and/or adivalent pyrene radical, the radicals R⁷, R⁸, and R⁹ are monovalent,tetravalent or trivalent aromatic or heteroaromatic groups,respectively, and the radicals U, which are identical within a repeatingunit, are an oxygen atom, a sulfur atom or an amino group which carriesa hydrogen atom, a group having 1-20 carbon atoms, preferably a branchedor unbranched alkyl or alkoxy group, or an aryl group as a furtherradical.
 3. The polymer of claim 1 further comprising being doped withacid.
 4. The polymer of claim 2 further comprising being doped withacid.
 5. The polymer of claim 1 wherein said polymer has a specificvolume resistance of not more than 100 Ωcm at 25° C.
 6. The polymer ofclaim 2 wherein said polymer has a specific volume resistance of notmore than 100 Ωcm at 25° C.
 7. The polymer of claim 1 wherein saidpolymer swells by less than 100% in deionized water at a temperature of90° C.
 8. The polymer of claim 2 wherein said polymer swells by lessthan 100% in deionized water at a temperature of 90° C.
 9. The polymerof claim 1 wherein said polymer has an ion exchange capacity of between0.5 meq/g and 1.9 meq/g, based in each case on the total mass of thepolymer.
 10. The polymer of claim 2 wherein said polymer has an ionexchange capacity of between 0.5 meq/g and 1.9 meq/g, based in each caseon the total mass of the polymer.
 11. A process for preparing thepolymer of claim 1, comprises the step of reacting one or more precursorpolymers, which individually or in total contain the functional groupsa), b), and d), wherein a) and b) being defined as per claim 1 and d)designating sulfinate groups of the general formula (6)

with a compound of the general formula (7) YL_(m)  (7) where L is aleaving group and m is an integer greater than or equal to 2, whereinR¹, M, and Y being defined per claim
 1. 12. The process of claim 11,wherein said precursor polymers comprise a polymer mixture of 1) atleast one precursor polymer having functional groups a), 2) at least oneprecursor polymer having functional groups b), and 3) at least oneprecursor polymer having functional groups d).
 13. The process of claim11 wherein said precursor polymers comprise 1) at least one precursorpolymer having functional groups a) and b) and 2) at least one precursorpolymer having functional groups d).
 14. The process of claim 11 whereinsaid precursor polymers comprise 1) at least one precursor polymerhaving functional groups a) and d) and 2) at least one precursor polymerhaving functional groups b).
 15. The process of claim 11 wherein saidprecursor polymers comprise 1) at least one precursor polymer havingfunctional groups a) and 2) at least one precursor polymer havingfunctional groups b) and d).
 16. The process of claim 11 wherein saidprecursor polymer comprises at least one polymer having functionalgroups of the general formula of a), b), and d).
 17. The process ofclaim 11, wherein said precursor polymer being dissolved in apolar-aprotic solvent, preferably in N,N-dimethylformamide,N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide orsulfolane and the solution is reacted with a halogen compound, withstirring.
 18. The process of claim 17 further comprising a) the polymersolution is spread as a film onto a substrate and b) the solvent isevaporated where appropriate at an elevated temperature of more than 25°C. and/or under a reduced pressure of less than 1000 mbar to give apolymer membrane.
 19. The process of claim 11 further comprising a) thepolymer is treated in a first step with an acid and b) the polymer istreated in a further step with deionized water, the polymer beingtreated where appropriate with an aqueous alkali prior to the firststep.
 20. The process of claim 11 further comprising the polymer beingdoped with an acid, preferably with phosphoric acid.
 21. Anelectrochemical cell, preferably in secondary batteries, electrolysiscells, and in polymer electrolyte membrane fuel cells, especiallyhydrogen fuel cells and direct methanol fuel cells comprising a membranemade of the polymer of claim
 1. 22. A process for membrane separationwherein membrane separation comprises gas separation, pervaporation,perstraction, reverse osmosis, nanofiltration, electrodialysis, anddiffusion dialysis comprising the steps of providing a membrane made ofthe polymer of claim 1.